Models for the single-vehicle preemptive pickup and delivery problem

In this paper, we study a variant of the well-known single-vehicle pickup and delivery problem where the demands can be unloaded/reloaded at any node. By proving new complexity results, we give the minimum information which is necessary to represent feasible solutions. Using this, we present integer linear programs for both the unitary and the general versions. We then show that the associated linear relaxations are polynomial-time solvable and present some computational results.